Absorption Rates and Biologic Effects of Pellets of a-Estradiol and a-Estradiol Benzoate in Women

Summary and Conclusions

A comparative study of the absorption rates and duration of biologic effectiveness of implanted pellets of a-estradiol and a-estradiol benzoate was made in a series of 14 cases. This study revealed that the average percent absorption rate, per 30 days, of a-estradiol pellets was 4.85% (= 473 rat units per day), as compared to 1.72% (=113 rat units per day) for pellets of a-estradiol benzoate. The duration of biologic and therapeutic effects was definitely longer in the a-estradiol series. It is concluded, on the basis of these studies, that the fibrous capsule which forms about the pellets progressively decreases the rate of absorption of the hormone, so little being absorbed finally that no demonstrable morphologic or therapeutic effect is produced. Furthermore, because of the fact that absorption of the hormone in effective amounts ceases when only a relatively small amount of the pellet has been absorbed, it is concluded that the implantation of pellets (weighing 15 to 25 mg) of a-estradiol and a-estradiol benzoate is not a satisfactory method of administering estrogens clinically.

We wish to gratefully acknowledge the technical assistance of Mr. A. A. Salmon.